HENAGAR, Ala. — In a Senate race full of will-he-or-won’t-he dramas, President Trump settled one last week at the White House when he expressed support for Roy S. Moore.

But nearly a week after Mr. Trump essentially offered his renewed endorsement for Mr. Moore, who has been accused of sexual misconduct or unwanted advances involving teenage girls, the president’s words and tweets seem to have done little to stabilize or strengthen Mr. Moore’s campaign.

Instead, Mr. Moore and his supporters are already finding the outer boundaries of the White House’s tepid embrace — and, more crucially, the limits of just how much Mr. Trump’s support means in a state where he is widely popular.

“The average voter in Alabama doesn’t pay much attention to outsiders, to out-of-state support,” said the state auditor, Jim Zeigler, a Republican who has endorsed Mr. Moore.

That go-it-alone attitude has helped power Mr. Moore’s political career past decades of controversies, including his two removals, in effect, as chief justice of the Alabama Supreme Court. And indications are that the outcome of Mr. Moore’s campaign will be settled by what happens in Alabama, not what Mr. Trump says in Washington.

Mr. Trump already knows something about the limits of his influence in Alabama politics. He and the country’s top Republicans repeatedly endorsed Senator Luther Strange, Mr. Moore’s leading rival, in their primary election, only to see Mr. Strange lose by nine percentage points.

Mr. Trump then promptly endorsed Mr. Moore, whom he called “a really great guy who ran a fantastic race.” But the misconduct allegations, which Mr. Moore has denied, have left the campaign gasping and underfunded in the weeks before the Dec. 12 election.

And Mr. Trump may not do much else to aid Mr. Moore. The White House signaled on Monday that Mr. Trump will not use one of the most potent symbols of presidential power — Air Force One touching down somewhere along the campaign trail — to help Mr. Moore. The White House press secretary, Sarah Huckabee Sanders, said that Mr. Trump “is not planning any trip to Alabama at this time, and, frankly, his schedule doesn’t permit him doing anything between now and Election Day.”

The White House’s approach has left Mr. Moore’s campaign with only so much of a political tailwind, even in a state where Mr. Trump won 62 percent of the vote last year.

Abandoned by most of the country’s leading Republicans, except for Mr. Trump, Mr. Moore retreated on Monday night to a rural pocket of Alabama to make his case to voters.

In a speech that was occasionally homespun and sweepingly defiant, Mr. Moore made few references to Mr. Trump, but he summoned themes that are popular among his supporters: opposition to abortion and transgender rights, increased military spending and a harder approach to immigration. He recited Kipling, and he lashed out at his opponents and the allegations swirling around him.

“This is simply dirty politics, and it’s a sign of the immorality of our time,” he told a standing room-only crowd in Henagar, a city of about 2,300, during his first rally since Mr. Trump came to his defense.

Later, he added: “I’m going to take off some gloves and show the truth in this campaign.” He did not describe his plans and offered no evidence of malfeasance by his critics.

The race took another bizarre twist during the day when The Washington Post reported that it had apparently been the target of a two-week effort to plant an unsubstantiated story about Mr. Moore.

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“This is simply dirty politics, and it’s a sign of the immorality of our time,” Mr. Moore told a standing-room crowd on Monday in Henagar, Ala.CreditBrynn Anderson/Associated Press

The Post, which reported the first claims alleging sexual misconduct by Mr. Moore earlier this month, said it was approached by a woman who claimed to have conceived a child with Mr. Moore when she was 15. The Post was unable to corroborate the story and did not publish it, instead confronting the woman with questions about her claims.

According to The Post, the woman denied working for any organization that targets reporters, but she was observed on Monday at the offices of Project Veritas, a conservative organization that tries to embarrass media organizations and other institutions using deceptions and hidden cameras. (The group has previously targeted The New York Times.)

In Alabama, even with the limits on Mr. Trump’s involvement, Mr. Moore’s allies were scrambling to put Mr. Trump’s words in front of voters. And if Mr. Trump’s support for Mr. Moore is to shape the outcome, it is most likely to sway voters in places like Henagar, in DeKalb County, which last voted for a Democratic presidential candidate in 1976 and where Mr. Trump won 83 percent of the vote last fall.

Yet many voters near the site of Mr. Moore’s rally Monday night made up their minds about him long ago. At the Pro Source Tool Center, where Christmas decorations were on display along with gleaming tool bits, Roger Nix, 78, and Juanita Timmons, 79, had already decided to support Mr. Moore well before Mr. Trump stood behind his candidacy.

“I’m proud that he’s doing it,” Ms. Timmons said, but she added, “I had already voted for Moore to begin with, and I was going to do it again.”

Those who remained undecided, like Rachel Heard, were so deeply conflicted over the question of Mr. Moore’s alleged misconduct that they said a presidential endorsement did not yield much clarity.

“Whether he’s in his political party or whatever,” she said, “you get into people being in each other’s pockets, sweeping things under the rug.”

“A lot of people are swayed by politicians and famous people, and I would rather make the decision on my own,” said Ms. Heard, 35, a hair stylist at the Rustic Strand Salon.

Ms. Heard voted for Mr. Trump, but his support for Mr. Moore had not, she said, inched her any closer to a judgment on the veracity of the allegations against Mr. Moore.

“It hasn’t been settled yet,” Ms. Heard said, adding that Mr. Moore had been accused of “evil” behavior and that if she remained unsure by the Dec. 12 election, she might not vote at all.

Still, some of Mr. Moore’s most prominent supporters will take Mr. Trump’s backing any way they can get it, even if they believe it will have only a marginal influence.

“Roy Moore is going to win with or without that endorsement,” said Ed Henry, a state representative who was the co-chairman of Mr. Trump’s campaign in Alabama. “But it will give some encouragement to people who may have been sitting on the fence.”

Separately, Mr. Zeigler, the state auditor, suggested that the president’s support offered a measure of cover for Republican activists or officeholders who were inclined to back Mr. Moore but were unnerved by the allegations against him.

“The president’s support helps in an unusual sort of way: It signals other conservative-thinking people that it’s O.K. for them to come out with Judge Moore and to vote for Roy Moore,” Mr. Zeigler said.

But Mr. Moore — and, for that matter, many of his longstanding supporters — have not always had such of a view of the power of a presidential endorsement.

“President Trump is well-liked in Alabama, no doubt,” Mr. Moore said in an interview in August, when he and Mr. Strange were fighting for the Republican nomination. “But I don’t think that endorsement is going to do anything.”

A version of this article appears in print on , on Page A12 of the New York edition with the headline: Alabama Senate Race Is Test of Trump’s Reach. Order Reprints | Today’s Paper | Subscribe